The present invention relates to a timing chain wound between members which require a synchronous rotation. The timing chain of the present invention is wound, for example, between a crank sprocket and a cam sprocket of an engine for a vehicle, and is used for the synchronous rotation of a crank shaft with a cam shaft. Alternatively, the timing chain of the present invention can be wound between a crank sprocket and a balancer sprocket of an engine for a vehicle, and used for the synchronous rotation of a crank shaft with a balancer shaft.
A timing chain used for the synchronous rotation as mentioned above typically employs a sprocket having timing marks and a timing chain having timing marks. The timing marks are made to register when the timing chain is wound about the sprocket for achieving the synchronous rotation.
Incidentally, generally, the timing marks of the timing chain are provided by a method in which some marks are imposed on a single plate prior to construction of the timing chain. There is a further method of applying some marks to the timing chain by a plating treatment to provide timing marks. In this method, however, because gases generated during the plating treatment, for example, hydrogen, should be removed, and addition of a baking treatment is necessary to prevent the lowering of fatigue strength, the process management should naturally be severe, and the production efficiency is extremely bad.
The applicant has previously proposed a timing chain applied with timing marks by a color baking coating as disclosed in Japanese Patent Laid-Open No. 242829/1997. In this timing chain, timing marks obtained by the color baking coating are applied to outer plates of a part composing the timing chain, which is composed endlessly together with other plates.
However, according to these prior art practices the outer plates having timing marks are prepared via a manufacturing process separately from other outer plates. Therefore, it is necessary to store, as stock, outer plates having timing marks and outer plates having no timing marks for every type of timing chain. This poses a problem in that many steps for managing parts constituting the timing chain are necessary, and the securing of storage areas for the respective parts is very wasteful.
Further, since coated outer plates are assembled with other plates, the coated outer plates have to be incorporated into the specific parts in the midst of construction of the timing chain. Normally, the specific parts are positioned on one side of the timing chain though different according to the type of the timing chain, and are positioned at two places in the chain. Accordingly, when the timing chain is constructed, it is necessary to specify the surface and back of the timing chain, as well as to specify the predetermined position in the chain, and then to assemble the coated outer plates. Further, since the coated outer plates have to be switched to the other outer plates to compose the timing chain, a number of steps are required to assemble the timing chain.
Furthermore, since, after the entire surfaces of the respective outer plates have been coated, during construction of the timing chain, when the outer plates are pressed into the pins upon assembly of the timing chain, the coating is sometimes peeled off. When the coating is partly peeled off, the external appearance of the timing chain becomes worsened. When the coating is completely peeled off, the timing marks cannot be discriminated, and failure to assemble them between the members, for which the synchronous rotation is required, occurs.